This invention relates to a process for the production of sulfur containing organosilicon compounds by phase transfer catalysis techniques. The process involves reacting the phase transfer catalyst with the aqueous phase components of the process to create an intermediate reaction product, which is reacted with a silane compound to form a product mixture, and then the organosilicon compound is separated from the product mixture.
Sulfur containing organosilicon compounds are useful as reactive coupling agents in a variety of commercial applications. In particular, sulfur containing organosilicon compounds have become essential components in the production of tires based on rubber vulcanates containing silica. The sulfur containing organosilicon compounds improve the physical properties of the rubber vulcanates containing silica resulting in automotive tires with improved abrasion resistance, rolling resistance, and wet skidding performance. The sulfur containing organosilicon compounds can be added directly to the rubber vulcanates containing silica, or alternately, can be used to pre-treat the silica prior to addition to the rubber vulcanate composition.
Numerous methods have been described in the art for the preparation of sulfur containing organosilicon compounds. For example, U.S. Pat. No. 5,399,739 by French et al. describes a method for making sulfur-containing organosilanes by reacting an alkali metal alcoholate with hydrogen sulfide to form an alkali metal hydrosulfide, which is subsequently reacted with an alkali metal to provide an alkali metal sulfide. The resulting alkali metal sulfide is then reacted with sulfur to provide an alkali metal polysulfide which is then finally reacted with a silane compound of the formula Xxe2x80x94R2xe2x80x94Si(R1)3, where X is either chlorine or bromine to produce the sulfur-containing organosilane.
U.S. Pat. Nos. 5,466,848, 5,596,116, and 5,489,701 describe processes for the preparation of silane polysulfides. The ""848 patent process is based on first producing sodium sulfide by the reaction of hydrogen sulfide with sodium ethoxylate. The sodium sulfide is then reacted with sulfur to form the tetrasulfide, which is subsequently reacted with chloropropyltriethoxysilane to form 3,3xe2x80x2-bis(triethoxysilylpropyl)tetrasulfide. The ""116 patent teaches a process for the preparation of polysulfides, without the use of hydrogen sulfide, by reacting a metal alkoxide in alcohol with elemental sulfur, or by reacting sodium metal with elemental sulfur and an alcohol, with a halohydrocarbylalkoxysilane such as chloropropyltriethoxysilane. The ""701 patent claims a process for the preparation of silane polysulfides by contacting hydrogen sulfide gas with an active metal alkoxide solution and subsequently reacting the reaction product with a halohydrocarbylalkoxysilane such as chloropropyltriethoxysilane.
U.S. Pat. No. 5,892,085 describes a process for the preparation of high purity organosilicon disulphanes. U.S. Pat. No. 5,859,275 describes a process for the production of bis (silylorganyl) polysulphanes. Both the ""085 and ""275 patents describe anhydrous techniques involving the direct reaction of a haloalkoxysilane with a polysulphide.
U.S. Pat. No. 6,066,752 teaches a process for producing sulfur-containing organosilicon compounds by reacting sulfur, an alkali metal, and a halogenalkoyxsilane in the absence of a solvent or in the presence of an aprotic solvent.
Most recently, U.S. Pat. No. 6,140,524 describes a method for preparing short chain polysulfide silane mixtures of the formula (RO)3SiC3H6SiC3H6Si(RO)3 having a distribution where n falls in the range of 2.2xe2x89xa6nxe2x89xa62.8. The ""524 method reacts metal polysulfides, typically Na2Sn with a halogenopropyltrialkoxysilane having the formula (RO)3SiC3H6X wherein X is a halogen, in alcohol solvent.
Alternative processes for the preparation of sulfur-containing organosilanes have been taught in the art based on the use of phase transfer catalysis techniques. Phase transfer catalysis techniques overcome many of the practical problems associated with the aforementioned prior art processes for producing sulfur-containing organosilicon compounds. Many of these problems are related to the use of solvents. In particular, the use of ethyl alcohol can be problematic because of its low flash point. Additionally, it is difficult to obtain and maintain anhydrous conditions necessary in many of the aforementioned prior art processes on an industrial scale.
Phase transfer catalysis techniques for producing sulfur-containing organosilicon compounds are taught for example in U.S. Pat. Nos. 5,405,985, 5,663,396, 5,468,893, and 5,583,245. While these patents teach new processes for the preparation of sulfur containing organosilicon compounds using phase transfer catalysis, there still exist many practical problems with the use of phase transfer techniques at an industrial scale. For example, there is a need to control the reactivity of the phase transfer catalyst in the preparation of sulfur-containing organosilanes so as to provide efficient, yet safe reactions that can be performed on an industrial scale. Furthermore, there is a need to improve the final product stability, appearance and purity. In particular, the phase transfer catalysis process of the prior art results in final product compositions containing high quantities of un-reacted sulfur species. These un-reacted sulfur species can precipitate in stored products with time causing changes in product sulfide distribution.
It is therefore an object of the present invention to provide an improved process for the production of sulfur containing organosilicon compounds based on phase transfer catalysis techniques.
It is a further object of the present invention to provide a process for producing sulfur containing organosilicon compounds based on phase transfer catalysis techniques that result in a final product composition of greater stability, purity, and appearance.
The present invention provides a process for the production of sulfur containing organosilicon compounds by phase transfer catalysis techniques. The process involves reacting a phase transfer catalyst with the aqueous phase components of the process to create an intermediate reaction product, which is then reacted a silane compound to form a product mixture. The sulfur containing organosilicon compound is then separated from the product mixture.
The improvement of the present invention is characterized by adding the phase transfer catalyst to the aqueous phase prior to mixing the aqueous phase with the silane compound for the reaction and by additional separation steps. The improvements of the present invention result in a process that is controlled and operable on an industrial scale and produces a final product composition of greater purity and appearance.